Field of the Invention
The disclosure relates to communications systems in general, and to techniques for determining time-of-flight between nodes of a communications system, in particular.
Description of the Related Art
In general, two-way ranging includes cooperative techniques for determining a time-of-arrival or time-of-flight of a signal between two nodes. The time-of-flight information may be used to determine a distance between nodes, position, velocity, acceleration, etc. However, sources of error in conventional time-of-flight measurement techniques limit the accuracy of any subsequent calculations based thereon. Time-of-flight refers to the latency of a transmission from a near-end transceiver to a far-end transceiver. Typical time-of-flight estimates are based on transmissions of digital signals, e.g., based on digital signals prior to conversion into analog signals for transmission and digital signals received after being converted from received analog signals. Those typical time-of-flight estimates do not include an accounting for delay of analog circuits (e.g., analog transmitter, analog receiver). However, the latencies of the analog circuits can be non-trivial. Another conventional time-of-flight measurement technique assumes that analog transmitter and analog receiver latency is below a predetermined value, ttransceiver, which may be predicted from transmitter and receiver designs and target manufacturing process information. Variation of actual transceiver latency from the predetermined value (e.g., due to manufacturing variances, environmental conditions, aging, or signal strength) introduces error in a time-of-arrival measurement or other metric determined based on the latency information. In an exemplary localization application, the transceiver latency error, |ttransceiver−ttransceiver_actual|=Δttransceiver, corresponds to a ranging error of at least approximately catmosphere×Δttransceiver, where catmosphere is the rate of propagation of electromagnetic waves through air under typical atmospheric conditions. The transceiver latency error may introduce a substantial amount of error to a localization measurement in some applications. Accordingly, improved techniques for improving accuracy of time-of-flight measurements are desired.